Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $88.58   4.704%   $92.7468   $92.75   $92.75   $92.70  
  Purchase #2 $113.60   4.342%   $118.5325   $118.53   $118.55   $118.50  
  Purchase #3 $26.32   9.265%   $28.7585   $28.76   $28.75   $28.80  
  Purchase #4 $19.32   12.489%   $21.7329   $21.73   $21.75   $21.70  
  Purchase #5 $59.57   6.194%   $63.2598   $63.26   $63.25   $63.30  
  Purchase #6 $123.83   8.846%   $134.784   $134.78   $134.80   $134.80  
  Purchase #7 $204.65   6.444%   $217.8376   $217.84   $217.85   $217.80  
  7 purchase totals = $635.87       $677.6521   $677.65   $677.70   $677.60